BLOGS

Earlier this year in National Geographic, I wrote about how feathers evolved long before flight. This timing naturally raises the question, how did feathered dinosaurs take to the air? My article was accompanied by a picture from the University of Montana lab of Ken Dial, who argues that before dinosaurs flew, they flapped their wings to help them travel up and down inclines. While not all experts accept Dial’s hypothesis, it has the undeniable strength that he can gather evidence for it in living birds, rather than just inferring behavior from fossils alone.

This video shows some of the astonishing climbs birds can make with the help of some wing flapping. It’s a mix of lab climbs and footage from the wild, with an evolutionary tree of birds.

This is a skill that takes time for birds to develop, as shown in this video below. Dinosaurs might have gradually acquired the skill as well, as their arms evolved into more bird-like wings.

Dial argues that this flapping would also help on the way down, too. Here’s a young bird leaping to the ground, and flapping its wings to control its fall.

By the time dinosaurs had evolved the ability to use feathers to assist in climbs, they would have already developed the wing stroke used by birds today for true flight, as this video shows.

Even without full flight, Dial argues, flapping feathered wings would have given little feathered dinosaurs the boost they needed to escape hungry predators. And this behavior could have served as an evolutionary bridge from the land to the air.

Ken Dial’s work on WAIR is fantastic. It has become fundamental in discussions about avian flight origins. Ken also gives some of the best scientific presentations I have ever seen; one of his talks at the Annual Meeting of the Society of Vertebrate Paleontology was so spectacular that he was given a standing ovation.

All that said, I happen to be one of the scientists who is skeptical of the role of WAIR, specifically, in the origin of flight. It is likely that early birds and/or bird-like dinosaurs (basal avialans, to those familiar with the jargon) did not possess an upstroke with the proper kinematic range to allow a WAIR ascent (this would issues related to angle of attack, direction of lift, and mitigation of vorticity delay, otherwise known as the “Wagner Effect”).

Still, the work by Dial et al. is a shining example of how the aerodynamic forces produced by wings can be used for mobility functions other than flight. This alternative usage model, in a general sense, is being increasingly accepted as a fundamental part of the origin and early evolution of avian flight.

Why in the world would anyone doubt that wings are useful even if they are incapable of flight? I live with a parrot, and when she was young I had her wings clipped so that she could not fly. She still used them for climbing inclines all the time. As she got older and gained more experience, I let her feathers grow out and she has been fully flighted for some time. She *still* uses her wings to assist climbing all the time! I guess none of these scientists have ever lived with a bird?

Oh, by the way, with the assist of wing-flapping, my parrot can climb a vertical wooden dowel.

(Granted, observing how modern birds use their wings does not prove how their pre-flight ancestors used their wings. Also, I do not live with a flightless bird, but there *are* flightless parrots and I’d bet good money that they also use their wings to assist climbing. Anybody know for sure?)